Caffeine (1,3,7-trimethylxantine) is among alle-lopatic connections making inhibiting impact on various intracellular processes of vegetable organ-isms which is confirmed by the results of many la-boratory researches. However, in a number of ex-periments it was shown that this substance can also act as growth factor positively influencing cell fission. The research objective was studying the influence of caffeine on viability of seeds and the development of sprouts of Linum usitatissimum L. The seeds of flax were affected by caffeine in vari-ous concentrations for the assessment of its influ-ence on early stages of ontogenesis. Daily during 144 h experiment the weight, length of the main root and hypocotyl and also the ratio of their lengths were defined. For the third and sixth day the energies of germination and total viability of seeds were estimated respectively. It was estab-lished that caffeine in the concentration of 0.025-0.10 % had negative impact on the growth and de-velopment of sprouts: the length of sprouts de-creased in the process of increasing concentration of solution, and the development of root system was exposed to more intensive influence, than the development of elevated part of plants therefore the ratio of root length changed hypocotyl length. At the same time low concentration of caffeine (0.025-0.05 %) practically did not render statistically signif-icant effect on seeds viability. It was established that negative or positive effect from the impact of 1,3,7-trimethylxantine on growth and development of plants depended mainly on specific accessory of studied plants, cultivation conditions, and also ex-istence (absence) of other accompanying connec-tions possessing allelopatic properties.